1. Field of the Invention
The invention herein described relates to a novel paper cutting mechanism of an electronic printing device with the reverse motion of the paper feed mechanism operating the cutting mechanism. In particular, this machine offers several advantages over the prior an in terms of simplicity, economy of design, maintainability, and reliability. Prior machines have often used complex linkages, expensive cutting blades, separate motor, active enabling sources, require precision components and/or assembly, were difficult to maintain, had long strokes thereby limiting their cutting width, or requiring high power.
Additionally, the invention herein disclosed, is equally applicable to a variety of electronic printing technologies. These include but are not limited to thermal, thermal transfer, dot matrix, and ink jet technologies. It is common in these technologies to move the paper with a stepping motor power source. Motors of this type have the ability to rotate in both the clockwise and counterclockwise directions. In most applications it is only necessary to feed print media in the forward direction, thereby freeing the opposite direction of rotation for powering other devices such as a paper cutting mechanism. The present invention takes advantage of unidirectional paper motion and uses the counter-rotating motion to power the cutting mechanism through a pair of one-way clutches such as those manufactured by The Torrington Company of Torrington, Conn.
2. Prior Art
U.S. Pat. No. 4,211,498, invented by Munetaka Shimitzu et al., describes a cutting device having a blade with a plurality of triangular shaped cutting edges. This cutter design is comprised of a reciprocating bar which serves as the power source. Said power source is connected to the cutting mechanism by a complex solenoid operated interposing linkage having numerous wear points. To start the cutting cycle, the interposer is retracted by the solenoid. A linkage located at the power source end of a pivoted blade drive arm rotates into the path of the oscillating bar and causes the blade drive arm to pivot in the cutting direction while pushing the cutting blade forward. To retract the blade, the solenoid interposer is released and springs retract the blade to its non-operating position. This design has weaknesses in that it has a high degree of mechanical complexity, resulting in many wear points, significant assembly labor, poor maintainability, and is not positively retracted thereby making it prone to jamming. Additionally, it is difficult to align the slit in the print media support with the blade as they are on opposite sides of the mechanism. This promotes poor cutting, blade wear, and a propensity to jam.
U.S. Pat. No. 4,544,293, invented by Dean H. Cranston et al., illustrates a matrix printing mechanism with an integral scissors style cutting blade. The printhead is longitudinally driven across the paper by a barrel cam rotated in its primary direction by a D.C. motor. The cutting mechanism is driven by the printhead carriage cam shaft when rotated in its secondary direction. The cutting mechanism is coupled to the drive gear train through a one-way clutch. When the cam is rotated in the secondary direction the one-way clutch engages a gear with a pin which operates in a slot on a pivoted lever. As this gear rotates, it rides in the slot and pivots the blade actuating arm which in turn pivotally actuates the scissors-like pair of cutting blades. Scissors type blades require very long strokes and high cutting forces to complete the cutting cycle. Additionally, this type of blade configuration has a propensity to separate at the free end of the moving blade, thereby causing the paper to roll between the blades and jam the printer. This condition becomes decidedly worse as the edges of the blades wear. The Blade Drive gear is a sector gear so that the possibility of over-travel of the blade can be eliminated. However, if such over-driving were to occur, the last meshing teeth would likely be damaged by the ensuing skipping action. This design as well as the Shimitzu patent requires a spring return and as previously stated could be prone to become jammed closed, thereby assuring paper feed jamming. Additionally, the motor must be run in the opposing direction to facilitate the blade return to the home position. This design invokes a severe printing throughput penalty as the printhead is moved away from its home reference position during the cutting cycle. Also, using the cam in the manner stated precludes any implementation of intelligent printing. An additional drawback is that if the user wishes the output to be incompletely severed, this condition can only occur at one point at the open end of the blades. This may be undesirable to the user.
U.S. Pat. No. 4,491,046, invented by Hiroshi Hosogaya, teaches the design of a scissors action cutter similar to the Cranston patent and, additional provides a protection mechanism against blade damage from hard objects. The drive arm is driven by a cam and uses a return spring to bring the moveable blade to the home position. The pivot of the blade is constructed as a "U" shape and the blade is spring biased to keep the "U" pivot in contact with the pivot pin fixed in the stationary blade support. If a hard object obstructs the motion of the blades, the pivot separates from the pivot pin to prevent blade damage. Additionally, the design improves on the Cranston design in that it provides a loading force to keep the blades together at the open end.